For me, Mental Toughness isn't as much as a slog because there are more sets, more variety, and it's 15 minutes shorter. I really like that first set in MT--the ten minute one where you shift every 30 seconds. I have to admit that the last set on that DVD is one I dread---the "Roger goes over 200 beats per minute set." He used that one to wrap up Have Mercy, if I'm not mistaken.

Endurance Booster is better for endurance, I think, because of the sets are longer and seem relentless when you're doing them. When you shift into easier gears, you are supposed to increase your cadence accordingly so it really isn't easier. And the breaks between reps are short (although between the sets, you get 2 minutes recovery).